Method and apparatus for inspecting defects

ABSTRACT

Laser lights having a plurality of wavelengths from DUV to VUV range are used to inspect defects of a pattern at high speeds and in a high sensitivity using high light-output lasers, while solving a temporal/spatial coherence problem caused by using lasers as light source. This reduces the laser light temporal/spatial coherence. Further, to correct chromatic aberration caused by illumination with VUV and DUD lights, the lights of the VUV and DUV wavelengths are arranged in a coaxial illumination relation. The chromatic aberration left uncorrected is detected such that a detection optical path is branched into two optical path systems corresponding to respective wavelengths and an image sensor is placed on an image plane of each wavelength.

BACKGROUND OF THE INVENTION

[0001] The present invention is related to an optical system, a defectinspecting method and a defect inspecting apparatus with employment ofthis optical system, and a utilizing method for effectively utilizinginspection information, while the optical system is employed so as toinspect and observe defects and extraneous-material defects of patternsformed on substrates by way of thin-film manufacturing processes whichare typically known in semiconductor manufacturing steps andmanufacturing steps of flat panel displays.

[0002] To detect defects of very fine patterns formed on substrates byway of thin-film manufacturing processes, images having high imagequality are necessarily required, the focuses and contrasts of whichhave been adjusted in high precision.

[0003] In the defect inspection field for instance, JP-A-2000-323542discloses the image detecting method of objects as the conventionaltechnique capable of acquiring such high grade images. This conventionaltechnique is to detect images as follows. That is, while a broadbandwhite light source is employed as a light source and focal points aredefined at different places along a Z direction with respect to each ofwavelength ranges of white light, two systems of image sensors arearranged in such a manner that the image sensors are focused onto both asurface layer and a rear plane of an object in the case that the objectowns stepped portions. In two systems of these image sensors, focusingpositions on the object planes are made different from each other alongan optical axis direction in accordance with longitudinal chromaticaberration of an objective lens. As a consequence, images of differentplanes of the object are detected by the respective image sensors byutilizing the longitudinal chromatic aberration of the objective lens.It should be understood that as to a detecting optical path for twosystems of the image sensors, band-pass filters are arranged in opticalpaths defined by that an optical path is branched and thereafter thebranched optical paths are reached to the respective image sensors insuch a manner that such light corresponding to the respectivelongitudinal chromatic aberration may penetrate through these band-bassfilters.

[0004] The above-described conventional technique is directed to such atechnical idea that images of different planes on a wafer are detectedby employing two systems of the image sensors, and then images focusedon the respective image sensors are employed. As a consequence, thisconventional technique is not to produce a new image from the imagesdetected by two systems of these image sensors, but is directed so as toselect any one of the images detected from two systems of these imagesensors so that this selected image is used in the defect inspection.However, in thin-film manufacturing processes typically known assemiconductors, flatting (planer) process operations are carried out asto wafer surfaces based upon the CMP (Chemical Mechanical Polishing)process operation. Thus, the thin-film manufacturing processes need notdetect images at different heights on a wafer by employing theabove-explained two image sensors. Also, even when stepped portions areformed on wafers, since structures of semiconductor logic products arecomplex, the selective use of such images detected by two systems ofthese image sensors cannot be employed.

[0005] To detect defects of very fine patterns in high precision,wavelengths of illumination light must be made shorter. Generallyspeaking, laser light sources are necessarily required in order tosecure sufficiently large amounts of illumination light of light sourceshaving short wavelengths for inspection purposes. However, in the casethat such laser light sources are employed as illumination, interferenceproblems of laser light may occurs. In other words, there are problemsas to temporal/spatial coherence, problems of interference noises whichare produced by thin-films formed on surfaces of samples, problems ofcontract between very fine patterns and background patterns, problems ofilluminance fluctuations of pulse illumination light, and the like.

SUMMARY OF THE INVENTION

[0006] In accordance with the present invention, while a laser having alarge light amount is employed, defects of patterns can be inspected ina high sensitivity by solving the above-described problems as to thetemporal/spatial coherence occurred because of using the laser in theabove-explained illumination light source.

[0007] In other words, the present invention is so arranged by thatbasic resolution of an optical system may be improved by shortening awavelength of illumination light. The wavelength to be shortened isdirected to DUV (Deep Ultra-Violet) light up to VUV (VacuumUltra-Violet) light. As a light source used in these wavelength ranges,there is an FO laser (wavelength being 157 nm) as the VUV range. Inorder to employ these laser light as a defect inspecting optical systemfor illumination purposes, there are two technical aspects. As onetechnical aspect, brightness fluctuations of detected images andcoherencies are reduced, which are caused in connection with filmthickness fluctuations in optically transparent interlayer insulatingfilms which are formed on a surface of an object. The brightnessfluctuations caused by the film thickness fluctuations of the insulatingfilms were reduced by employing such an arrangement that light having aplurality of wavelengths is illuminated. Also, a temporal coherence canbe also reduced by illuminating the light having such pluralwavelengths.

[0008] However, as to the light in the range from DUV to VUV, since anitre material having high transmittance is restricted, for instance, insuch a case that both the VUV light and the DUV light are coaxiallyilluminated, chromatic aberration cannot be corrected. As a consequence,while the light having the respective wavelengths is coaxiallyilluminated, such a chromatic aberration which cannot be corrected isdetected in such a manner that a detection optical path is branched intotwo optical paths corresponding to the wavelengths, and then, imagesensors are arranged on image planes of the respective wavelengths. As aresult, as to an object plane (same plane) for a subject matter, twoimages are detected which are focused within two wavelength ranges.Since these two images are electrically synthesized with each other(namely, new image is produced by employing two images), it is possibleto detect such an image having high resolution, from which noise couldbe reduced in view of defect inspection.

[0009] These and other objects, features and advantages of the inventionwill be apparent from the following more particular description ofpreferred embodiments of the invention, as illustrated in theaccompanying drawings.

BRIEF DISCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a schematic block diagram for indicating an entirearrangement of a defect inspecting apparatus according to the presentinvention.

[0011]FIGS. 2A and 2B are a front view for showing a basic structure ofan optical path difference optical system using polarization and a tableshowing the number of circulating times in the circulating optional pathand the ratio between reflected light (R) and transmitting light (T) atPBS 7 c respectively.

[0012]FIG. 3 is a perspective view of a PBS for explaining a calculationof an amplitude of light which penetrates through the PBS.

[0013]FIG. 4 is a front view for representing an optical path differenceoptical system according to another embodiment of the present invention.

[0014]FIG. 5 is a schematic block diagram for indicating an arrangementof an illumination optical system capable of reducing coherence.

[0015]FIG. 6A is a side view of a rotary diffusing plate, and FIG. 6B isa front view of the rotary diffusing plate.

[0016]FIG. 7 is a graphic representation for showing a relationshipbetween a film thickness of SiO₂ and reflectance.

[0017]FIG. 8 is a front view for indicating a radiation polarizer.

[0018]FIG. 9 is a schematic block diagram for representing anarrangement of an optical system for correcting deviation ofillumination light along a vibration direction thereof.

[0019]FIG. 10 is a front view for indicating a polarizer.

[0020]FIG. 11 is a schematic diagram for schematically showingpolarization conditions of both zero-order light and high-orderdiffraction light at a surface of a wafer and a pupil plane of anobjective lens.

[0021]FIG. 12 is a schematic diagram for schematically showingpolarization conditions of both zero-order light and high-orderdiffraction light at a surface of a pupil plane of an objective lens.

[0022]FIG. 13 is a schematic block diagram for indicating an arrangementof an optical system for controlling amplitudes of the zero-order lightand of the high-order diffraction light.

[0023]FIG. 14A indicates an image of a wiring pattern when is observedby a conventional optical system, and FIG. 14B shows an image of awiring pattern which is observed by an optical system of the presentinvention.

[0024]FIG. 15A represents an image of a focal position on the rear sideof an objective lens in the case that a line-and-space pattern isobserved by the conventional optical system, and FIG. 15B indicates animage of a focal position on the rear side of the objective lens in thecase that the line-and-space pattern is observed by the optical systemaccording to the present invention.

[0025]FIG. 16 is a graphic representation for indicating a relationshipbetween transmittance of zero-order light and pattern contrast.

[0026]FIG. 17A is a plan view for representing a die formed on a wafer,FIG. 17B indicates a signal of a portion of an image of a die, takenalong a line A-A of the die image, which is obtained when the die isobserved by the conventional optical system, and FIG. 17C indicates asignal of a portion of an image of a die, taken along a line A-A of thedie image, which is obtained when the die is observed by the opticalsystem of the present invention.

[0027]FIG. 18 is a schematic block diagram for showing an arrangement ofan illuminance fluctuation correcting unit for illumination.

[0028]FIG. 19 is a schematic block diagram for indicating an arrangementof an observation optical system on which an illuminance fluctuationfunction is mounted.

[0029]FIG. 20 is a flow chart for describing process flow operations ofa pattern defect inspecting signal according to the present invention.

[0030]FIG. 21 is a perspective view for schematically indicating anarrangement of a production information managing system with employmentof a defect inspecting apparatus according to the present invention.

[0031]FIG. 22 is a diagram for showing an example of information of aninspection result which is outputted from the defect inspectingapparatus according to the present invention to the productioninformation managing system.

DESCRIPTION OF THE EMBODIMENTS

[0032] In the present invention, light existing in the ranges from DUV(Deep Ultra-Violet) to VUV (Vacuum Ultra-Violet) is employed asillumination light so that the basic resolution may be increased.Inventors of the present invention have fined out such a fact that sincepolarization light is employed as illumination, even when very narrowdefects occur, images having higher resolution (high contrast) may beacquired. However, when a laser light source is employed forillumination, a detection sensitivity would be lowered by receiving anadverse influence caused by so-called “stray light”, namely laser lightis reflected on a surface of an optical component and the reflectedlaser light is entered into a detector. In accordance with the presentinvention, in order to avoid this adverse influence of the lowereddetecting sensitivity caused by this stray light, a plurality of opticalpaths having different optical path lengths are provided in anillumination optical system, and then, a detection is made of imagesproduced by illumination light which passes through the respectiveoptical paths to be reached on a sample.

[0033] Also, in order to reduce an adverse influence of a film thicknessof an optically transparent film formed on a surface of a sample, suchan arrangement is made. That is, as to chromatic aberration which cannotbe corrected by a lens system, an optical path on a detection opticalpath is branched every wavelength, and images at the respectivewavelengths are detected so as to realize a system for illuminatingillumination light having a plurality of wavelengths from a coaxialdirection. These images which have been detected every wavelength aresynthesized with each other, and an image processing operation iscarried out as to these synthesized images as a single image, so that adefect is detected. Also, in order that images can be detected which maygive a merit for detecting a defect, an amplitude of zero-order lightwhich is direct-reflected on a wafer is suppressed, and a balancebetween this suppressed amplitude of the zero-order light and anamplitude of high-order diffraction light can be adjusted. Furthermore,either Brewster angle illumination or total reflection angleillumination has been employed as an illumination system capable ofreducing an adverse influence of thin-film interference.

[0034] One example of an embodiment mode of the present invention isshown in FIG. 1. Laser light emitted from a laser light source 2 andlaser light having a wavelength different from that of the above laserlight, emitted from another laser light source 3 are coaxially-processedby a dichroic mirror 8 so as to be formed as single laser light 4. Thislaser light 4 is entered into a polarizing beam splitter (will bereferred to as a “PBS” hereinafter) 7 to be split into a P-polarizedlight component and an S-polarized light component. The P-polarizedlight component passes through this PBS 7. The S-polarized lightcomponent is reflected on the PBS 7 and then is projected therefrom,while an optical axis of this S-polarized light component is bent alonga right angle direction. The S-polarized light component which isprojected while bending the optical axis thereof along the right angledirection is entered into an optical path difference optical system 10.The light of the S-polarized light component which is entered into theoptical path difference optical system 10 receives an optical pathdifference, and then is again coaxially-processed by a PBS 7 c with thelight which has been previously branched by the PBS 7. These plural setsof laser light pass through a spatial coherence reducing unit 15, andthereafter, penetrate through wavelength plates 50 and 51 havingdifference phase difference amounts and also an objective lens 20 toilluminate a wafer 1.

[0035] Among a plurality of light which have beenreflected/diffracted/scattered on patterns formed on the wafer 1, suchlight propagated within an NA (Numerical Aperture) of the objective lens20 is again captured by the objective lens 20, so that an optical imageis focused on an image plane. It should be noted that in an imagedetecting optical path, while a dichroic mirror 25 is arranged whichowns a similar branching characteristic to that of the above-describeddichroic mirror 5 arranged in the illumination system, optical imagesformed in the respective wavelengths are detected by image sensors 30and 35. This is because a nitre material of a lens is restricted inresponse to a wavelength of laser light, and chromatic aberration cannotbe connected, so that the image sensors are arranged at focusingpositions defined in response to the respective wavelengths of the laserlight sources 2 and 3.

[0036] In accordance with the present invention, in order that very finedefects having dimensions of on the order of 20 to 30 nm can be detectedwhich could be hardly detected in the conventional defect inspectingapparatus using the UV light (ultraviolet light: wavelength (λ)=about365 nm), either DUV light (deep ultraviolet light: λ=approximately 300to 180 nm) or VUV light (vacuum ultraviolet light: λ=approximately 180to 100 nm; in case of F2 laser, λ=157 nm), which have shorterwavelengths than that of the UV light, may be employed as theillumination light source. Also, in the case that a laser is employed asthe illumination light source, such a problem of interference of laserlight will occur due to high coherence owned by the laser. In accordancewith the present invention, in order to solve this problem,two-wavelength illumination is employed, so that temporal coherence islowered.

[0037] Image signals which are detected by two systems of the imagesensors 30 and 35 are converted by A/D converting circuits 52 and 53,respectively, into digital variable-density image data. In ordernormalize illuminance fluctuations sensed by an illuminance fluctuationmonitor 33 of laser light, these digital variable-density image data areentered into an illuminance fluctuation correcting circuit 60, so thatfluctuations in illumination light amounts may be normalized. Thedigital variable-density images, the illuminance of which has beencorrected respectively, are inputted into an image synthesizing circuit80 in order to synthesize a plurality of images with each other toproduce a single image. The image synthesizing circuit 80 forms asynthesized image by electrically summing, for example, two images toeach other. This synthesized image data is entered into an imageprocessing unit 85 so as to perform a calculation by which a defect ofthe image may be extracted. It should also be noted that this defectinspecting apparatus may be arranged in another mode. That is, no imagesynthesizing operation is carried out in the image synthesizing circuit80 in order that a defect may be inspected by employing such an imagedetected by any one of these two systems of the image sensors.

[0038] The defect information (namely, coordinate values and sizes ofdefects, classification results etc.) extracted by the image processingunit 85 is transferred to an operating computer 95 equipped with adisplay screen capable of displaying thereon defects. Also, informationsimilar to this defect information is stored into an inspectioninformation managing system 296. A θ-stage 110, a Z-stage 115, anX-stage 120, and a Y-stage 125, which mount the wafer 1, are controlledby a mechanical control unit (MC) 90. Also, the operating computer 95may operate the inspecting apparatus, and issues an instruction to themechanical control unit 90 in the case that this operating computer 95executes operations of a mechanism unit. Further, the operating computer95 may interface with an operator, for example, setting of inspectionconditions.

[0039] Also, in accordance with the present invention, a light sourceoperable in the VUV range is mounted. As a result, in order to minimizean attenuation of light within an optical path, such a region 38 ispurged which contains optical paths defined by that the laser lightemitted from the laser light source 2 and the laser light emitted fromthe laser light source 3 are reached to the image sensors 30 and 35,respectively. It should also be noted that a working distance betweenthe objective lens 30 and the wafer 1 is set to an atmosphericenvironment. As a consequence, the wafer 1 may be handled underatmospheric environment, so that cost of the defect inspecting apparatuscan be reduced, and also, the wafer transportability thereof can beimproved.

[0040] Also, in accordance with this embodiment mode, the descriptionhas been made by employing the laser light sources. Alternatively, theselaser light sources may be readily replaced by lamp light sources.Alternatively, since such illumination light having a wavelength shorterthan, or equal to 200 nm is employed, resolution may be improved andvery fine defects having dimensions of approximately 30 to 20 nm may bedetected.

[0041] The optical path difference optical system 10 will now beexplained with reference to FIG. 1 and FIGS. 2A and 2B. The laser lightwhich has been emitted from the laser light sources 2 and 3 having thedifferent wavelengths and has been coaxially-processed by the dichroicmirror 8 is split into the transmission light (P-polarized light) andthe reflection light (S-polarized light) by the PBS 7. The S-polarizedlight component reflected by the PBS 7 is conducted to the optical pathdifference optical system 10. Since this S-polarized light passesthrough a ½-wavelength plate 8, such a phase difference is given to insuch a manner that this S-polarized light may become P-polarized lightwith respect to the PBS 7 a of a circulating optical path which isformed by the PBS 7 a, the PBS 7 b, a total reflection mirror 101, andanother total reflection mirror 102, and then, penetrates through thePBS 7 a.

[0042] The penetrated light is reflected by both the total reflectionmirrors 101 and 102, and then passes through a ½-wavelength plate 11, sothat such a phase difference is given in such a manner that aP-polarized light component may be equivalent to an S-polarized lightcomponent with respect to the PBS 7 b provided on the output side of thecirculating optical path. As a result, as to such a light which isentered into the PBS 7 b provided on the output side of the circulatingoptical path, the S-polarized light component is reflected to the sideof the PBS 7 a, and then is again entered into the circulating opticalpath. In contrast to this S-polarized light component, the P-polarizedlight component penetrates through the PBS 7 b and then is entered intoa ½-wavelength plate 12, and such a phase difference is given in such amanner that this P-polarized light becomes S-polarized light withrespect to the PBS 7 a, and thereafter, is entered into the PBS 7 c. TheS-polarized light which has been reflected by this PBS 7 and has beenentered into the PBS 7 c after being penetrated via the circulatingoptical path is coaxially-processed with such a P-polarized light whichhas passes through the PBS 7 and then has been entered into the PBS 7 c,so that the coaxially-processed polarized light may become illuminationlight for illuminating an object 1.

[0043] It should also be understood that within the circulating opticalpath, the splitting operation between the reflection and thetransmission is repeatedly performed in the PBS 7 b in the secondcirculating time and succeeding circulating times, and the reflectedS-polarized light is furthermore repeatedly circulated. This is shown ina Table shown in FIG. 2B. In addition, a difference between an opticalpath length of S-polarized light which is reflected by the PBS 7 and isentered via the circulating optical path into the PBS 7 c and an opticalpath length of P-polarized light which passes through the PBS 7 and isdirectly entered into the PBS 7 c may have such a distance which islonger than, or equal to the below-mentioned coherent distance of thelaser light 4, and the temporal coherence of the light which has beencoaxially-processed by the PBS 7 c may be reduced. It should also benoted that a formula capable of calculating a coherent distance “L” isindicated in an expression (1): $\begin{matrix}{L = \frac{\lambda \quad c^{2}}{\Delta \quad \lambda}} & \left( {{expression}\quad 1} \right)\end{matrix}$

[0044] The coherent distance “L” is directly proportional to a square ofa central wavelength “λc” of illumination light, and isinverse-proportion to a wavelength width of the illumination light. Forinstance, a coherent distance “L” in the case that an F2 laser (λ=157nm) for generating vacuum ultraviolet light (VUV light) is employed asthe illumination light source is equal to several tens of nm.

[0045] In this case, FIG. 3 shows an example of a calculation of asplitting ratio by the PBS 7 for splitting the incident laser light intothe P-polarized light and the S-polarized light. The P-polarized lightcomponent of the laser light 4 which is entered into the PBS 7penetrates through the PBS 7, and the S-polarized light componentthereof is reflected. As a result, in the case that the entered laserlight 4 corresponds to linearly polarized light having a vibration planeat an angle of “θ” with respect to the vibration direction of theP-polarized light, a light amount of transmitting polarized light may beobtained based upon the following expression (2): $\begin{matrix}{T = \frac{\left( {\cos \quad \theta} \right)^{2}}{\left( {\cos \quad \theta} \right)^{2} + \left( {\sin \quad \theta} \right)^{2}}} & \left( {{expression}\quad 2} \right)\end{matrix}$

[0046]FIG. 4 shows an example of an optical path difference opticalsystem 10′ established based upon another method. In the case of FIG. 4,such a structure that the laser light 4 is entered into the PBS 47 andthen the S-polarized light component is reflected and the P-polarizedlight component passes through the PBS 47 is identical to the structureexplained in FIG. 1 and FIG. 2. In the structure of FIG. 4, theS-polarized light component of the laser light 4 which is reflected onthe PBS 47 is projected to the side of a first optical path differenceoptical system 17. This first optical path difference optical system 17is constituted by two sheets of total reflection mirrors 103 and 104. Insuch a structure, the S-polarized light which is entered in the firstoptical path difference optical system 17 is reflected by two sheets ofthese total reflection mirrors 103 and 104, and is entered into the PBS47, and then is again coaxially-processed with the P-polarized lightwhich passes through the PBS 47. In this case, an optical path length ofthe first optical path difference optical system 17 has a differencelonger than, or equal to the coherent distance with respect to anoptical path length of the P-polarized light which passes through thePBS 47 and is directly entered into the PBS 47 a.

[0047] Since the light which is synthesized by the PBS 47 a penetratesthrough a ¼-wavelength plate 48, this light is converted into circularlypolarized light. The circularly polarized light is entered into the PBS47 b so as to be again split into a P-polarized light component and anS-polarized light component. This S-polarized light component is enteredinto a second light path different optical system 18. The S-polarizedlight which is entered into this second optical path difference opticalsystem 18 is reflected by two sheets of total reflection mirrors 105 and106, then is entered into the PBS 47 c so as to be again synthesizedwith the P-polarized light component which has passed through the PBS 47b.

[0048] An optical path length of this second optical difference opticalsystem 18 is longer than the above-described optical path length of thefirst optical path difference optical system 17 by such a distanceequivalent to the coherent distance of the laser light 4.

[0049] In this case, the S-polarized light which will be entered intothe second optical path difference optical system 18 corresponds to suchlight which is split from the circularly polarized light converted bycausing both the P-polarized light component and the S-polarized lightcomponent which have been synthesized with each other by the PBS 47 a topass through the ¼-wavelength plate 48. As a result, an amplitude ofthis S-polarized light becomes a half of an amplitude of each of thelight (S-polarized light component) which has penetrated through thefirst optical path difference optical system 17, and the light(P-polarized light component) which has not passed through this firstoptical path difference optical system 17.

[0050] In this case, it is so assumed that a difference between theoptical path length of the S-polarized light which passes through thefirst optical path difference optical system 17 and the optical pathlength of the P-polarized light which does not pass through the firstoptical path difference optical system 17 but is directly reached fromthe PBS 47 to the PBS 47 a is equal to “L1”, whereas a differencebetween the optical path length of the S-polarized light which passesthrough the second optical path difference optical system 18 and theoptical path length of the P-polarized light which does not pass throughthe second optical path difference optical system 18 but is directlyreached from the PBS 47 b to the PBS 47 c is equal to “L2”. In thiscase, four systems of rays are formed by the first optical pathdifference optical system 17 and the second optical path differenceoptical system 18. Differences among optical path lengths of these raysare longer than the coherent distance, respectively. These rays are: (1)a ray (optical path difference 0) which does not pass through an opticalpath length of two systems; (2) a ray (optical path difference L1) whichhas passed through only the first optical path difference opticalsystem; (3) a ray (optical path difference L2) which has penetratedthrough only the second optical path difference optical system; and (4)a ray (optical path difference L1+L2) which has passed through both thefirst and second optical path difference optical systems. An amplitudeof each of these four systems of rays is, in principle, equal to eachother. However, in an actual case, there is more, or less a differenceamong these amplitudes in such a case, this balance may be adjustedbased upon setting condition of the ¼-wavelength plate.

[0051] As previously explained, since the four systems of such lighthaving the large optical path differences are employed as theillumination light, the adverse influence of the interference caused bythe stray light (namely, such light which is unnecessarily reflected onoptical components, and is not reached to wafer, but is directly reachedto image sensors) appearing on the image sensors 30 and 35 can bereduced. As a result, levels of the noise can be lowered, and levels ofthreshold values of the defect inspection can be suppressed to lowlevels, so that the defect inspection can be realized in highsensitivities.

[0052] Furthermore, in FIG. 1 and FIGS. 2A and 2B, the embodiment withemployment of the ½-wavelength plate has been described. Also, in FIG.4, the embodiment with employment of the ¼-wavelength plate has beenexplained. A similar effect may be achieved even when any one of thesewavelength plates is employed, depending upon setting methods of thesewavelength plates. As a consequence, the arrangements shown in FIG. 2and FIG. 4 merely constitute one example, and therefore, variousapplications thereof may be conceived.

[0053] Referring now to FIG. 5, a detailed description is made of thespatial coherence reducing unit 15 of the laser light. The laser light 4which has passed through either the optical path difference opticalsystem 10 or the optical path difference optical system 10′ is enteredinto a beam expander 151 so as to expand a beam diameter thereof, andthereafter, is entered into a first diffusing plate 150, so that thedirectivity of the laser light 4 is diffused.

[0054] Next, this diffused light passes through a first lens system 152,and thereafter is entered into a fly eye lens 155 which is constructedof a rod lens. A point light source group is formed at a projection endof the fly eye lens 155 in response to a diffusing degree of the fistdiffusing plate 150, and this point light source group constitutes asecondary light source. Light emitted from the secondary light source isentered into a second diffusing plate 160. This second diffusing plate160 is constructed in a rotatable manner, and is rotary-driven by amotor 165. When the second diffusing plate 160 is rotated by the motor165, since a phase of light which is entered into the second diffusingplate 160 is temporally disturbed, a coherence may be reduced. The lightwhich has passed through this second diffusing plate 160 forms asecondary light source image at a position of a projecting pupil 21 ofthe objective lens 20 by way of a second lens system 153. As a result,this may construct such a Koehler illumination in which an illuminancedistribution becomes uniform on an object plane. It should be noted thatthe temporal/spatial coherence of the laser light can be reduced bycombining the previously-indicated optical path difference opticalsystems, the first and second diffusing plates, and furthermore the flyeye lens 155 with each other.

[0055] In this case, FIGS. 6A and 6B represent an example of a structureof the second diffusing plate 160. The diffusing plate 160 is arrangedin a doughnut shape. This diffusing plate is rotated by the motor 165,so that a phase of illumination light may be temporally distributed. Arotation period of this diffusing plate 160 may be desirablysynchronized with a time period in which an image is acquired. Forinstance, in the case that an image acquisition time period is selectedto be “T”, the rotation period of the diffusing plate 160 is set toT1/n. In this formula, symbol “n” is a natural number.

[0056]FIG. 7 represents a relationship between a film thickness of amodel and reflectance of this model in which an electric insulating filmis formed on surface of the wafer 1. As to the insulating film, SiO₂ isemployed as the model. It should be noted that the illumination light ismonochromatic color having a wavelength of 193 nm, and incident lightwas calculated as to two sorts of illumination of 0 to 50°, andillumination of 50 to 60° which becomes near the Brewster angle (57.5°).Also, refractive indexes of the insulating film and SiO₂ correspond tothat of the wavelength of 193 nm.

[0057] In the illumination of 0 to 50° (random polarized light),reflectance thereof is vibrated in connection with an increase in filmthicknesses. This is caused by thin-film interference. When the filmthickness is changed, an optical path difference between light reflectedon the surface of the insulating film and light which is entered intothe thin film and is derived therefrom into an atmosphere is changed,the reflectance is vibrated by way of the change in the filmthicknesses. This vibration is fluctuated within a width of 3% to 28% asto the reflectance, namely, there are 25% of vibration widths. Thisreflectance variation indicates brightness of an optical image formed onan image plane. As a consequence, in such a case that patterns formed onthe wafer 1 are compared with each other for an inspection purpose, iffilm thicknesses of insulating films are different from each other intwo regions for comparisons, then a brightness difference is increased.In the case that this film thickness variation of the insulating filmsdoes not own the fatal characteristic with respect to a device, thisbrightness fluctuation constitutes noise while defects are detected.

[0058] Conversely, in the case that the film thickness variation own thefatal characteristic as to a device, since this film thickness variationis required to be detected, if a variation of reflectance with respectto the film thickness is large, then this film thickness variation maybe easily detected. However, in an example of a semiconductormanufacturing step, since this film thickness variation does not own thefatal characteristic as to a device, if a vibration width of reflectanceis large in response to a film thickness of an insulating film, thenthis film thickness variation may constitute noise in view of inspectionsensitivity. As a method for reducing this reflectance variation width,Brewster angle illumination has been employed in accordance with thepresent invention. This Brewster angle illumination implies such anillumination that when P-polarized light is illuminated at a specificangle, this P-polarized light is not reflected on a boundary between aninsulating film and air, but the entire P-polarized light may penetratetherethrough. As a result, amplitude splitting does not occur whichcauses thin-film interference, but there is no reflectance variation inconnection with film thickness variations. In FIG. 7, a calculationresult in the case that the P-polarized light is illuminated at anincident angle of 50° to 60° is also indicated.

[0059] In this illumination in the vicinity of this Brewster angle, avariation of reflectance may be reduced to approximately 0.5% to 3%. Asa consequence, the P-polarized light is illuminated at an incident anglein the vicinity of the Brewster angle, so that brightness fluctuationsoccurred in connection with the film thickness variations of theinsulating film can be reduced. As a result, since the noise produced inthe inspection may be reduced, the defect detecting sensitivity may beimproved. Next, a description will now be made of an example forilluminating light at the Brewster angle with reference to FIG. 5. Anincident antle of illumination light may be determined based upon ashape of a secondary light source image which is formed at a position ofa pupil 21 of the objective lens 20

[0060] To illuminate light at an angle in the vicinity of an incidentangle 57° which constitutes the Brewster angle, a secondary light sourceimage having a ring shape is required to be imaged at the position ofthe pupil 21. As a consequence, since an aperture stop 156 having a ringshape is arranged in the vicinity of the projection edge of the fly eyelens 155, the light can be illuminated at such an incident angle in thevicinity of the Brewster angle. It should also be noted that thisaperture stop 156 may be arranged at any other positions than theprojection edge of the fly eye lens 155, namely, at a position in thevicinity of a conjugate position in such a case that this conjugateposition is present with respect to the projection pupil 21 of theobjective lens 20. Also, only such a light which isreflected/diffracted/scattered at an angle of approximately 57° withrespect to the optical axis is reached to an image sensor, so thatfluctuations in reflectance which are caused by the thin-filminterference can be reduced. This alternative case is realized asfollows: That is, while a spatial filter (not shown) is arranged ateither the position of the pupil 21 of the objective lens 20 or theposition on the side of the conjugate image (on the side of imagesensor), only such light which is reflected/diffracted/scattered at nearthe incident angle of 57° with respect to the optical axis is caused tobe reached to the image sensor among the light which has beenreflected/diffracted/scattered on the wafer 1 (detection of Brewsterangle). In case of this Brewster angle detecting the incident angle ofthe illumination light need not be limited only to the Brewster angle.

[0061] While both the Brewster angle illumination and the Brewster angledetecting methods have been described. Alternatively, the Brewster angleillumination may be readily combined with the Brewster angle detectingsystem. Also, as to the aperture stop 156 and the spatial filter, otheraperture stops/spatial filters having different shapes may be installed,based upon such a fact as to whether or not the wafer 1 has theinsulating film.

[0062] Next, with respect to a measure capable of illuminatingP-polarized light, an example with employment of a radial-shapedpolarizer will now be explained with reference to FIG. 8.

[0063] Although laser light emitted from a light source is linearlypolarized light, the polarized light is disturbed by a first diffusingplate and a second diffusing plate, and the like. As a result, in orderto illuminate the wafer 1 by P-polarized light, the polarized light mustbe vibrated in a radial form at the projection pupil plane 21 of theobjective lens, while the optical axis is set as a center. As thismeasure, a filter (radial-shaped polarizer) 130 is provided at such aconjugate position with respect to the pupil position 21 of theobjective lens 20, so that the P-polarized light can be illuminated onthe wafer 1. This filter 130 may penetrate therethrough illuminationlight along the radial direction as to the vibration direction of theillumination light, while the optical axis is positioned at a center. Itshould also be understood that even when this filter 130 is located atthe pupil position 21 of the objective lens 20, or in an illuminationoptical path located other than the conjugate position of this pupilposition 21, otherwise, in a detection optical path, an advantageouseffect may be achieved. Also, in a case that both the first and seconddiffusing plates are not arranged in the illumination system, and alsoin such a case that deviation is still left along the vibrationdirection even: after the illumination light has passed through thediffusing plates, even if the above-described filter 130 is arranged,uniform polarized-light illumination cannot be realized. As aconsequence, a method for eliminating deviation along the vibrationdirection is shown in FIG. 9. It should also be noted that a diffusingplate is not illustrated in this example.

[0064] A beam diameter of the linearly polarized light 4 emitted fromthe laser light source 2 is expanded by a beam expander 190. Theexpanded linearly polarized light is entered into a ½-wavelength plate58, and thus, the polarized light is rotated at a speed 4 times higherthan the rotation frequency of this ½-wavelength plate 58 and then, therotated polarized light is projected therefrom. It should also be notedthat this ½-wavelength plate 58 is rotary-driven by a motor 185.

[0065] The light which has penetrated through the ½-wavelength plate 58furthermore passes through ½-wavelength plates 58 a, 58 b, and 58 c. Atthis time, every time this light penetrates through the respective½-wavelength plates 58 a, 58 b, 58 c, a rotation speed of a vibrationplane becomes 4 times. It should also be noted that although the½-wavelength plates 58 a, 58 b, 58 c are fixed in this example, these½-wavelength plates 58 a, 58 b, and 58 c may be rotated in a similar tothe ½-wavelength plate 58. The light which has passed through these½-wavelength plates 58, 58 a, 58 b, and 58 c becomes rotary polarizedillumination light, and then is reflected on a beam splitter 19. Thereflected illumination light is entered into an objective lens 20 so asto be illuminated on the wafer 1. It should also be noted that in orderto illuminate the wafer 1 by the P-polarized light by employing therotary polarized illumination light, the radial-shaped polarizer 130shown in FIG. 8 is arranged between the spatial coherence reducing unit15 and the beam splitter 19 as indicated in FIG. 9. It should also beunderstood that as an arrangement for arranging the radial-shapedpolarizer 130 in the detection optical path, this radial-shapedpolarizer 130 may be arranged between the beam splitter 19 and the imagesensor 30.

[0066] Also, as the illumination method for not causing the thin-filminterference, there is a total reflection angle illuminating method fortotally reflecting illumination light on a surface of a substrate. Aformula (expression 3) for calculating a total reflection angle “θc”used to totally reflect illumination light on a substrate is given asfollows:

sin θc=n2/n1  (expression 3).

[0067] In this formula, symbol “n1” shows a reflective index within air,and symbol “n2” represents a reflective index of an insulating film.

[0068] In order to realize the total reflection illumination, anincident angle must be set to 90 degrees. It is practically difficult torealize this setting of the incident angle in view of a structure. As aconsequence, in order to increase reflectance on a surface of aninsulating film, while the incident angle is increased as large aspossible (namely, is approximated to 90 degrees), the surface of theinsulating film must be illuminated by using S-polarized light. Torealize the S-polarized light illumination, the vibration direction ofthe illumination light must be set to a circumferential direction on theplane of the pupil 21 of the objective lens 20, while the optical axisis set as a center. To realize this condition, such a polarizer 131having a characteristic shown in FIG. 10 may be arranged on theillumination optical path. Also, the description has been made of such afact that both the polarizers 130 and 131 shown in FIG. 8 and FIG. 10are arranged in the illumination optical path. Alternatively, even whenan analyzer (not shown) having a similar characteristic is arranged inthe detection system, an equivalent effect may be achieved. In thisexample, the TTL (Through The Lens) system for illuminating theillumination light through the objective lens 20 has been explained.Alternatively, a darkfield illumination system for illuminatingillumination light from an outer side of an objective lens may beconceived. This darkfield illumination system is referred to as“off-axis illumination.”

[0069]FIG. 11 shows polarized light by illumination light, polarizedlight of direct reflection light or regular reflection light (zero-orderlight), and polarized light of high-order diffraction light. It is soassumed that polarized light 201 of illumination light is vibrated alonga circumferential direction at the pupil plane 21. This lightilluminates a pattern formed on the wafer 1. It should also beunderstood that a semi-spherical portion 22 on the wafer 1 schematicallyindicates conditions of diffraction by the objective lens 20. Thezero-order light which is directly reflected on the wafer 1 ispropagated to a position which is symmetrical to the optical axis at thepupil position 21. At this time, the polarized light owns a vibrationplane along the same circumferential direction to that of theillumination light. In contrast, the diffraction directions of thehigh-order diffraction light are different from each other in responseto a direction of a pattern formed on the wafer 1. As a result, sincethe direction along which the high-order diffraction light is madedifferent with respect to the illumination light, a vibration direction210 of the high-order diffraction light at the pupil plane 21 becomes adifferent vibration plane with respect to the vibration direction 201 ofthe illumination light and the vibration direction 205 of the zero-orderlight. It should also be noted that the polarized light with respect tothe wafer 1 is identical to the illumination light, the zero-orderlight, and the high-order diffraction light, and is stored. This isschematically indicated in FIG. 12.

[0070] In FIG. 12, a vibration direction of illumination light at thepupil plane 21 of the objective lens 20 is indicated by 201. Adistribution of +1-order light is represented by 220, which is producedby a pattern on the wafer 1. Also, a distribution of −1-order light isdenoted by 221. In this case, among reflection light reflected from thewafer 1, which is caused by the illumination light having the vibrationdirection 201 at the pupil plane 21, the zero-order light which has beenagain captured by the objective lens 20 is reached to a position 205. Onthe other hand, the +1-order diffraction light is reached to 210. Atthis time, the vibration direction at the pupil plane as to thezero-order light is different from the vibration direction at the pupilplane as to the high-order diffraction light (note that vibrationdirections thereof are identical to each other with respect to wafer).As a result, in the case that the polarized light is illuminated, sincea polarization filter which may penetrate therethrough a large amount ofthe +1-order diffraction light is arranged in the detection opticalpath, the zero-order light may be suppressed and also the high-orderdiffraction light containing the +1-order diffraction light can beeffectively penetrated. Since this high-order diffraction light containsa larger amount of pattern information than that of the zero-orderlight, contrast of an optical image can be increased by effectivelydetecting the high-order diffraction light. Otherwise, the contrast ofthe optical image may be adjusted to desirable contrast.

[0071]FIG. 13 shows an example of realizing this contrast adjustment. Asto the linearly polarized light emitted from the laser light source 2,the S-polarized light thereof is reflected on the PBS 19 to constitutesuch an illumination light which is directed to the side of the wafer 1.This illumination light may become such an elliptically polarized lighthaving a desirable ellipticity and an azimuth angle of an ellipse bythat the azimuth angle of the ellipse is adjusted by a ½-wavelengthplate 50 and the ellipticity is adjusted by a ¼-wavelength plate 51.This illumination light is illuminated via the objective angle 20 ontothe wafer 1. The light which has been reflected/diffracted/scattered onthe wafer 1 is again captured by the objective lens 20, and passesthrough the ½-wavelength plate 50 and the ¼-wavelength plate 51, andthen is entered into the PBS 19. A ratio of zero-order light passingthrough the PBS 19 to the light entered into this PBS 19 may besubstantially determined based upon the ellipticity of the illuminationadjusted by the ¼-wavelength plate 51. In other words, when the¼-wavelength plate is adjusted so as to make the ellipticity ofillumination flat (namely, ellipticity is approximated to zero), a ratioof zero-order light which passes through the image sensors 30 and 35 islowered.

[0072] In contrast, a ratio of high-order diffraction light (±1-orderdiffraction light and like) which is reached to the image sensors 30 and35 is different in response to directivity of a pattern. As aconsequence, since both the ½-wavelength plate 50 and the ¼-wavelengthplate 51 are adjusted so as to properly set both the ellipticity and theazimuth angle of the ellipse, amplitudes of the zero-order light and ofthe high-order diffraction light which are reached to both the imagesensors 30 and 35 can be adjusted, so that the contrasts of the opticalimages formed on the image sensors 30 and 35 can be adjusted. As aconsequence, it is possible to form such an optical image capable ofadvantageously detecting defects, and thus, an improvement in theinspection sensitivity can be realized.

[0073]FIG. 14 indicates an example of images which were detected byemploying this optical system. FIG. 14A indicates that an image of thewafer 1 was detected by using the normal microscope, and FIG. 14Brepresents that the image of the wafer 1 was detected by employing theoptical system of the present invention. In FIG. 14A, lines an spaces,which are wired along a lateral direction, cannot be separated from eachother, so that shape failures of the wiring lines cannot be inspected.In contrast, in the image of FIG. 14B detected according to the presentinvention, since the lines and the spaces are separated in highercontrast, it can been understood that the inspection of the line andspace can be carried out in a higher sensitivity.

[0074] Also, FIG. 15 represents images of rear-sided focal positions(pupil positions: Fourier transforming plane) of the objective lens 20when lines and spaces which were formed along a longitudinal directionwere detected. FIG. 15A shows a pupil image of the normal illumination,and FIG. 15B indicates a pupil image obtained when the optical system ofthe present invention was employed. In FIG. 15A, optical strengths(brightness) of zero-order light distributed over the entire pupil aresubstantially equal to optical strengths (brightness) of ±1-orderdiffraction light distributed at right/left peripheral portions of thepupil. In contrast, as shown in FIG. 15B, in the case that the opticalsystem according to the present invention is employed, the ±1-orderdiffraction light can be detected by emphasizing the ±1-orderdiffraction light. As a result, it can be understood that the very finerpattern shapes can be restored into the optical images. As aconsequence, in accordance with the present invention, very finerpattern defects can be detected, as compared with that of such a casethat the normal optical system is employed.

[0075] Next, a method for adjusting pattern contrast of an optical imageby employing the optical system according to the present invention isillustrated in FIG. 16. An abscissa of this drawing indicates a ratio ofzero-order light which has been direct-reflected on the wafer 1penetrates through the PBS 19, whereas an ordinate thereof representspattern contrast on an image plane. Since transmittance of thezero-order light is converted, a ratio of the zero-order light to thehigh-order diffraction light on the image plane can be controlled, sothat the pattern contrast is changed.

[0076] In general, in order to improve contrast of an optical image, anamplitude of zero-order light is made substantially equal to anamplitude of high-order diffraction light. It should be noted that sincethis contrast corresponds to a difference between brightness of apattern portion and brightness of a space portion which constitutes abackground of this pattern portion, this contrast may be influenced byreflectance of the background and reflectance of the pattern portion.Also, a ratio of the zero-order light to the high-order diffractionlight may be influenced by a frequency and a material of a pattern, anazimuth angle of polarized light of illumination light, NA (NumericalAperture) of an objective lens, and the like. However, since theamplitude of the zero-order light and the amplitude of the high-orderdiffraction light are controlled, the pattern contrast can be adjustedunder desirable condition. It should also be noted that in order toadjust the contrast, both the azimuth angle of the ellipticallypolarized light and the ellipticity must be adjusted, and therefore,both the ½-wavelength plate 50 and the ¼-wavelength plate 51 must beconstructed in a rotatable manner (electrically rotatable).

[0077] Next, FIG. 17 shows effects of improvements in inspectionsensitivities in the case that the optical system of the presentinvention is employed. For instance, it is so assumed that such apattern indicated in FIG. 17A has been formed on the wafer 1 which isdirected for inspection. It should be noted that the pattern of FIG. 17Aschematically indicates one die 280 formed on the wafer 1. Within thispattern, there are a region 282 where a pattern pitch is coarse, aregion 286 where a pattern pitch is fine, and a region 284 where apattern pitch is medium. In this case, FIG. 17B shows such an examplethat these images were detected by using the normal optical system. FIG.17B represents an optical strength distribution, taken along a line A-Asown in FIG. 17A. In the region where the pattern pitch is coarse(namely, region where pattern frequency is low), sufficiently highcontrast can be obtained. However, when the pattern pitch becomes fine(when pattern frequency becomes high), the pattern contrast is lowered.

[0078] In defect inspection, the finer a pattern pitch is, the higherthe fatality due to defects becomes. Although the region where thepattern pitch is fine is wanted to be detected in view of the defectinspection, the normal optical system cannot realize this defectdetection. In contrast, in the case that the optical system according tothe present invention is employed, the amplitude ratio of the zero-orderlight to the high-order diffraction light can be adjusted, and asrepresented in FIG. 17C, while the pattern contrast of the region wherethe pattern pitch is coarse is maintained, the pattern contrast of theregion where the pattern pitch is fine can be increased. As a result,since the optical image with the high contrast can be obtained even whenthe fine pattern portion having the high totality is inspected, thedefects can be inspected under such a condition that the inspectionsensitivity is maintained in a high sensitivity.

[0079] Also, in accordance with the present invention, in the case thatthe region where the pattern pitch is coarse is inspected, both the½-wavelength plate 50 and the ¼-wavelength plate 51 are adjusted so asto make the contrast equivalent to that of the normal illumination, theimage can be detected without lowering the inspection sensitivity.

[0080] Next, a method for correcting illuminance fluctuations of laserlight is indicated in FIG. 18. For example, in the case that a laserlight source is a pulse oscillation, if there are strength fluctuationsin the respective pulses, then illuminance fluctuations will betemporally produced on the wafer 1. There is such a trend that when apulse oscillating frequency is increased, this illuminance fluctuationbecomes conspicuous. As a consequence, in order to execute inspection ina high speed, this problem of the illuminance fluctuation cannot beneglected.

[0081] Assuming now that the pulse frequency is constant, when aninspection speed is increased, a total number of pulses is decreasedwhich are illuminated so as to photograph one pixel of an image. As aresult, when strength variations are produced in the respective pulsesof illumination, brightness of detected images is different from eachother. This brightness difference cannot be discriminated from adifference in reflectances of patterns at a glance, resulting in noiseduring inspection. To correct this illuminance fluctuation, illuminanceof illumination must be monitored.

[0082] An arrangement shown in FIG. 18 is such an arrangement that whilethe wafer 1 is scanned in a constant speed along an X direction, animage is detected by using a one-dimensional image sensor. For instance,such a light which does not constitute the illumination light of thewafer 1 among laser light emitted from a laser light source is enteredinto a light amount monitor 55. Then, a light amount detected by thislight amount monitor 55 is inputted into an image illuminance correctingcircuit. Also, into this image illuminance correcting circuit, a digitalimage is entered, and this digital image is produced by A/D-convertingan image detected by the image sensor 30. Assuming now that illuminancewhen the image is detected is Iref(t) and brightness of the image isI(t, y), a light amount of each of pixels is corrected (Ical) based upona formula indicated by reference numeral 60 of FIG. 18. It should benoted that symbol “k” shows a coefficient. As a result, the illuminancefluctuations of the illumination can be normalized.

[0083]FIG. 19 schematically shows an arrangement equipped with anilluminance correcting function. In the case that laser light is pulseillumination, 1 pulse, or more pulses should be illuminated within astorage time period during which one pixels is detected. As aconsequence, an image acquisition by the image sensor 30 is preferablysynthesized with pulse illumination. However, in such a case that animage is detected by the one-directional image sensor 30, the imageacquisition by the one-dimensional image sensor 30 is required to besynthesized with a stage for scanning the wafer 1. As one example ofrealizing this synchronization, while both a signal 241 (X-direction)and another signal 242 (Y-direction) are employed which are obtained bydetecting a transport amount of the stage by using a distance measuringdevice (not shown) such as a linear scale, a synchronization signal 243generated from a synchronization signal generating device 240 is enteredinto a pulse control unit 250 in response to a preset image samplingperiod. A synchronization pulse signal 244 is outputted from the pulsecontrol unit 250 into a laser light pulse oscillating driver 230 inresponse to the synchronization signal 243, and then, laser light isoscillated in a pulse form from the laser light source 2 by receivingthis pulse synchronization signal 244.

[0084] Also, from the pulse control unit 250, the synchronization pulsesignal 245 is entered into a driver 31 of the image sensor 30, so thatsuch a control operation is carried out in which timing at which thelaser light is oscillated from the laser light source 2 may besynchronized with such a timing at which the image is acquired by theimage sensor 30. Although not described in FIG. 19, a similar controloperation is carried out as to both the laser light source 4 and theimage sensor 35.

[0085] Furthermore, the synchronization pulse signal 246 is alsosupplied from the pulse control unit 250 to an illuminance correctingunit 60. The illuminance correcting unit 60 acquires an illuminancedetection signal of laser light outputted from the illuminance monitor55 in synchronism with the timing at which the laser light is oscillatedfrom the laser light source 2 and also the timing at which the image isacquired by the image sensor 30, and then corrects the illuminancefluctuation with respect to the image acquired by the image sensor 30.

[0086] With employment of the above-described arrangement, it ispossible to solve the temporal/spatial coherence problem occurred byemploying the laser in the illumination light source, the interferencenoise problem caused by the thin film formed on the sample surface, thecontrast problem of the background pattern and the brightness, theilluminance fluctuation problem of the pulse illumination light, and thelike. Since the F2 laser (wavelength being 157 nm) corresponding to thevacuum ultraviolet light (VUV light) is employed as the light source,not only such a defect whose dimension is larger than, or equal to 50nm, but also such a very fine pattern defect having a dimension ofapproximately 20 to 30 nm can be detected in a high sensitivity and alsoin a high speed. It should also be noted that a pulse oscillation mustbe performed in a high frequency so as to detect an image in a highspeed by employing a pulse oscillation laser light source. This reasonis given as follows. That is, in order to detect an image, at least onepulse, or more pulses are required for illumination within a range ofthe storage time of the image sensor 30.

[0087] However, when energy of light which is illuminated on the wafer 1is high, a pattern formed on the wafer 1 may be damaged. As aconsequence, in order to acquire an image of one pixel, this image mustbe illuminated by using a plurality of pulses. As to the number of thesepulses, 30 pulses, or more pulses are required, depending upon amaterial. As a consequence, in order to detect an image in a high speed(for instance, 50 Gpps [Giga pixel per second]), a pulse oscillationmust be carried out in a high frequency. Ideally speaking, while acontinuous pulse oscillation may be preferably used, in the case ofpulse oscillation, the pulse oscillating frequency higher than, or equalto 50 KHz is required.

[0088] Alternatively, a TDI (Time Delay Integration) image sensor may becombined with the above-described arrangement, while this TDI imagesensor is capable of prolonging the storage time of the image sensor 30with maintaining the image acquisition speed. It should be understoodthat the TDI image sensor corresponds to such a system for storingelectron charges of CCD elements which are arranged along a scanningdirection of an image in synchronism with a speed at which an opticalimage of the wafer 1 is scanned, while these electron charges aretransferred. To realize the previously explained image detecting speedof 50 Gpps, 2000, or more stages capable of delaying/integrating theelectron charges are required. As a result, the high-speed imagedetecting operation can be realized, and thus, a high throughput of theinspecting apparatus can be realized.

[0089]FIG. 20 shows a flow chart for explaining process operationsexecuted in such a case that a pattern defect is inspected by employingthe defect inspecting apparatus shown in FIG. 1, which employs theabove-explained optical system of the present invention. The laser light4 emitted from the laser light sources 2 and 4 is conducted into theoptical path difference optical system so as to reduce coherences of aplurality of wavelengths (λ1, λ2), and this laser light 4 is againconverted into linearly polarized light. This linearly polarized lightis converted into elliptically polarized light by employing a wavelengthplate, and then, this elliptically polarized light is used via anobjective lens to illuminate the sample 1. At this time, illuminance ofthe illumination light is monitored. Light which has been reflected anddiffracted on the sample 1 by this illumination and then has beencondensed by the objective lens passes through the previously explainedwavelength plate. At this time, the zero-order light corresponding tothe direct-reflected light is converted into substantially learlypolarized light. Among these plural sets of light, a specific polarizedcomponent is conducted to a detection optical path.

[0090] In the detection optical path, an optical path iswavelength-split by a dichroic mirror, and optical images are formed onimage planes corresponding to the respective wavelengths. These opticalimages are detected by an image sensor so as to be photoelectricallyconverted respectively, so that variable-density information isoutputted by way of a video signal. This video signal is converted intoa digital signal. Next, brightness fluctuations of the image caused byilluminance fluctuations are corrected by employing such a signal formonitoring the illuminance of the illumination light.

[0091] Next, a plurality of digital images which have beenwavelength-split and detected are synthesized with each other. Thissynthesized image is entered into a positioning process unit. Also, thesynthesized image is also stored in a delay memory, and then istime-delayed in correspondence with pitches to be compared, andthereafter is entered into this positioning process unit. For example,in the case that a die comparison operation is carried out, thepositioning process unit executes the positioning operation between theimages which have been synthesized to be entered into this positioningprocess unit, and images of adjoining dies, which have been saved in thedelay memory. Next, in the positioning process unit, the images to whichthe positioning process operations have been accomplished are comparedwith each other for an inspection purpose, a feature amount ofdifferences is calculated so as to extract a defect, and then,information about the extracted defect is outputted. This defectinformation to be outputted may contain an image of a defect.

[0092] As previously explained, the inspecting apparatus, the managingmethods of the inspective result, and the utilizing methods of theinspective results have been described by indicating the variousembodiments. However, these indicated examples merely constitute oneexample of the present invention. Alternatively, other embodimentsrealized by combining these embodiments with other may be apparentlydefined within the technical scope of the present invention. Forinstance, the laser light may be readily replaced by a lamp lightsource.

[0093] Next, FIG. 21 schemaically indicates a system capable ofoperating a manufacturing line in a high efficiency by effectivelyutilizing the above-described inspecting apparatus. First, the wafer 1is conducted to the manufacturing line, and then is processed by amanufacturing apparatus group 29. In an intermediate step where aspecific processing operation has been carried out, an inspection isexecuted by an inspecting apparatus 300 according to the presentinvention. This inspecting apparatus 300 senses an abnormal state of apattern which has been manufactured in the preceding steps. In the caseof a multi-layer film, these steps are repeatedly carried out. A waferwhich has been processed through the above-described process steps isfinally accomplished, and then is further processed in post steps (diecutting, formation of lead wires, packaging, and the like), so that thewafer 1 may finally become a product. As to process abnormal statessensed by the respective inspecting apparatus, reasons of these abnormalstates and defect solution contents for these abnormal states areanalyzed by an analyzing apparatus, if necessary.

[0094] In accordance with the present invention, while the inspectionresults which are sequentially detected and the solution contents arestored in a production information managing system 296, such a systemmay be constituted by which the abnormal states may be discovered in anearlier stage and may be predicted so as to reduce failure products assmall as possible. This system is indicated in FIG. 11. Defectinformation detected by inspecting apparatus is inputted into both adefect information database 297 and a defect information collationsystem 292. Also, the defect information collation system 292 maycollate information with a yield/manufacturing apparatus informationmanaging system 299.

[0095] The production information managing system 296 shown in FIG. 21is constituted by the defect information database 297, the defectinformation collation system 298, and the yield/manufacturing apparatusinformation managing system 299. The defect information database 297stores thereinto defect information which has been detected after themanufacturing line was initiated. As the data, this defect informationdatabase 297 stores thereinto ADC (Auto Defect Classification) resultscorresponding to inspection results; both-images and coordinate valuesof defect portions which are detected in real time during inspections;and also, defect feature amounts calculated in the image processingoperation.

[0096] Also, with respect to these defects, the defect informationdatabase 297 stores such information as to defect occurrence reasons,defect solution results, and defect fatality. Also, the defectinformation collation system 298 collates/retrieves the various sorts ofinformation of the defect information database 297 which have beenpreviously acquired based upon inspection results (ADC result, image ofdefect portion, coordinate value of defect portion, defect featureamount) which are acquired by the inspection, and thus, judges fatalityof the defects. As a result, when it is so judged that the collateddefect has a high fatality, the defect information collation system 298establishes a correlative relationship between this judged defect andthe past defect data. In the case that this judged defect owns thecorrelative relationship with the past defect data, the productioninformation managing system 296 may propose a content of a defectsolution with reference to the defect solution information stored in thedefect information database 297.

[0097] Also, in the case that the judged defect corresponds to such adefect which has not yet occurred in the past, the analyzing apparatusanalyzes a cause of this defect, and also analyzes a defect generatingapparatus to execute, a defect solution. Also, since the defectinformation collation system 298 statistically establishes a correlativerelationship between the above-described defect information andtransitions of yield, maintenance conditions of the manufacturingapparatus, and the like, the defect information collation system 298 mayprobably disclose a causal relationship between the defect and theyield, and also a causal relationship between the defect and theapparatus condition. As a consequence, the production informationmanaging system 296 can grasp a prediction of the yield and themaintenance conditions of the apparatus, and may take a necessary defectsolution in an earlier stage in the case that lowering of the yield maybe predicted. Also, since data about these defect occurring conditionsand defect solution conditions are sequentially stored into the defectinformation database 297 and the yield/manufacturing apparatusinformation managing system 299, reliability of the data as well asreliability of the prediction can be improved.

[0098] As has been explained above, in accordance with the presentinvention, since the present invention can solve the temporal/spatialcoherence problem occurred by employing the laser in the illuminationlight source, the interference noise problem caused by the thin filmformed on the sample surface, the contrast problem of the backgroundpattern and the brightness, the illuminance fluctuation problem of thepulse illumination light, and the like, the defects of the patterns canbe inspected in the high speed and in the high sensitivities byemploying the laser having the large light amount. In particular, sincethe F2 laser (wavelength being 157 nm) corresponding to the vacuumultraviolet light (VUV light) is employed as the light source, such avery fine pattern defect having a dimension of approximately 20 to 30 nmcan be detected in a high sensitivity and in the high speed.

[0099] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiment is therfore to be considered in all respect asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. A method for inspecting a defect of a pattern, comprising the stepsof: irradiating polarized light to a sample where the pattern has beenformed; forming an optical image by reducing a light amount ofdirect-reflected light among reflection light reflected from said samplecaused by irradiating thereto said polarized light; detecting saidformed optical image; and detecting a defect of the pattern formed onsaid sample by employing a signal obtained by detecting said opticalimage.
 2. A defect inspecting method as claimed in claim 1 wherein: aplurality of polarized light having different wavelengths from eachother are irradiated to said sample.
 3. A defect inspecting method asclaimed in claim 1 wherein: said polarized light irradiated to saidsample corresponds to such a light produced by synthesizing a pluralityof polarized light with each other which penetrate through a pluralityof optical paths having different optical path lengths from each other.4. A method for inspecting a defect of a pattern, comprising the stepsof: irradiating polarized laser light to a sample where the pattern hasbeen formed; detecting an optical image of a surface of the sample towhich the laser light is irradiated so as to acquire an image signal;detecting a light amount of the laser light irradiated to said sample;correcting said image signal by employing a signal obtained by detectingthe light amount of said laser light; and detecting a defect of thepattern formed on said sample by employing said corrected image signal.5. A defect inspecting method as claimed in claim 4 wherein: said laserlight is pulse-oscillating laser light.
 6. A defect inspecting method asclaimed in claim 5 wherein: said sample is mounted on a table which iscontinuously transported along one axial direction; and oscillationtiming of said pulse-oscillating laser light, timing at which saidoptical image is detected so as to acquire the image signal, and timingfor correcting said image signal are synchronized with thetransportation of said table.
 7. A defect inspecting method as claimedin claim 4 wherein: laser light having a plurality of differentwavelengths is irradiated to said sample, and then optical images areseparately detected with respect to each of said laser light having thedifferent wavelengths.
 8. A method for inspecting a defect of a pattern,comprising the steps of: irradiating a plurality of laser light havingdifferent wavelengths from each other via an objective lens to a samplewhere the pattern has been formed; splitting reflection light reflectedfrom said sample to which said plurality of laser light are irradiatedevery said irradiated laser light having the plural wavelengths andforming optical images every said plural wavelengths; detecting saidformed optical images every said plural wavelengths; synthesizingdetection signals of said optical images with each other every saidplural wavelengths; and detecting a defect of said pattern by employingsaid synthesized detection signal.
 9. A defect inspecting method asclaimed in claim 8 wherein: said plurality of laser light arepolarized/split, and said split polarized laser light is irradiated tosaid sample.
 10. A defect inspecting method as claimed in claim 8wherein: said plurality of laser light are pulse laser light,respectively, and oscillating operations of said pulse laser light aresynchronized with detecting operations of said optical images.
 11. Amethod for inspecting a defect of a pattern, comprising the steps of:irradiating polarized light to a sample where the pattern has beenformed, said polarized light being produced by polarizing/splittingpulse-oscillating laser light having a wavelength shorter than 300 nm;forming an optical image by controlling a light amount ofdirect-reflected light among reflection light reflected from said samplecaused by irradiating thereto said pulse-oscillating laser light;detecting said formed optical image by a photoelectric convertingelement; and detecting a defect having a dimension of 30 nm to 20 nm ofsaid pattern by processing a detection signal of said detected opticalimage.
 12. A defect inspecting method as claimed in claim 11 wherein: awavelength of said pulse-oscillating laser light is 157 nm.
 13. A defectinspecting method as claimed in claim 11 wherein: said pulse-oscillatinglaser light is laser light emitted from a vacuum ultraviolet laser lightsource. 14-25 (canceled)